As the name implies you try to bring in people from the right side of the process to process phases on the left side. Develop (Developers) -> Test (Testers) -> Operate (Administrators) -> Use (Customers).
Shift-Right is nothing else what most companies do, if they do not yet have the benefits of automated testing or do not have dedicated testing resources. Key users are brought in, to test. They replace the testers. Therefore, the process changes like this: Develop (Developers) -> Test (Customers) -> Operate (Administrators) -> Use (Customers).
In comparison to Shift-Left, Shift-Right is mostly useful for internal rollouts or testing with small customers groups, because you need to have users that are so-called subject matter experts.